My goal is to nuke vesafb, and replace it with genfb in the i386 and
amd64 kernels. This is a prereq to having proper splash screen support.
I would like to check in the following changes to the x86 bootloader and
kernel. Any objections?

I will add some more just to be safe. Do you think there's any need to
make physaddr 64-bit?

- command_vesa should go into vbe.c since the other loaders will want it.

Will do.

Some observations:
- The growing collection of stubs is silly, it would be nice to copy the DOS
int86() call at some point in the future. Just an observation, I don't
object to adding the VESA stubs.

Yeah it's a royal pain, I'm not clued enough to pull it off though.

- x86_genfb_set_mapreg - probably safe to assume that it will work
everywhere but I'd like to get some test coverage with different hardware.

Not really sure how else to do this without bioscalls, I guess if it
doesn't work you are stuck with the rasops/splash colour palette unless
you boot in 16 or 32bpp modes. Alternately a native display driver will
have to beat out genfb and provide its own set_mapreg callback.

The other option here is to use VBE PMI where available, but I'm not
entirely sure how that would work on amd64.

I think this means setting fb console by default during the 6.0 cycle (in
boot.cfg). We could also look at ditching the vga driver and using the
simpler pcdisplay for fallback, and look at how it is going to interact
with drm. No point having pcdisplay+vga+genfb in the kernel.

I have checked in changed to genfb that makes it work with drm.

- We don't allow fb console to be hardwired into the loader binary with
installboot. But since it's really just an extension to the PC console
type, I don't think it matters.
Otherwise it looks OK to me.